Composite Actuators Research Articles

Stimuli-Responsive Shape Changing Commodity Polymer Composites and Bilayers.

Commodity polymers are produced in large volumes, providing robust mechanical properties at relatively low costs. The products made from these commodity polymers typically offer only static functionalities. Over the past decade, however, in the scientific literature, stimuli-responsive additives and/or polymer coatings have been introduced to commodity polymers, yielding composites and bilayers that change shape in response to light, temperature, and/or humidity. These stimuli responsive commodity polymers allow the marketing and sales of these otherwise bulk products as “high-end” smart materials for applications spanning from soft actuators to adaptive textiles. This Spotlight on Applications presents an overview of recent intriguing works on how shape changing commodity polymer composite and bilayer actuators based on polyamide 6, poly(ethylene terephthalate), polyethylene, and polypropylene have been fabricated that respond to environmental stimuli and discusses their potential applications.

Metal ion-promoted fabrication of melanin-like poly(L-DOPA) nanoparticles for photothermal actuation

Melanin-inspired polymers are currently the focus of growing interest for a wide range of applications ranging from energy to biomedical area. Whilst researchers have made numerous attempts to prepare and utilize polydopamine nanoparticles (PDA NPs), they have made limited progress in developing and discovering another typical functional mimic of natural melanin, poly (levodopa) (P(L-DOPA)) NPs, probably due to the lack of facile synthetic strategies towards satisfactory structural and functional control of melanin-like NPs. Herein, we reported a one-pot preparation method towards P(L-DOPA) NPs with good yields and controllable size/property in an aqueous solution assisted by various metal ions (i.e., Ni(II), Mg(II), Ca(II), Fe(III), Mn(II), Co (II), Zn(II) and Cd(II)). Interestingly, the resulting P(L-DOPA) NPs exhibited enhanced light absorption and photothermal behaviors compared with well-established PDA NPs, which can be employed to further fabricate kinds of photothermal composite actuators with promising performances such as folding, switching, and forward-moving. This study offers a facile and robust way to synthesize new synthetic melanins beyond PDA, and facilitates further functional discovery and evolution of melanin-inspired polymers and composites.

Least-squares method for laminated beams with distributed braided piezoelectric composite actuators

Piezoelectric ceramics are a very popular material in the field of actuator technology due to their unique piezoelectric properties. However, the brittle behavior of ceramics endangers the reliability of piezoelectric actuators. In this article, the three-dimensional braided piezoelectric composite is utilized to ameliorate the reliability and driving capability of piezoelectric actuators. The static analysis of laminated beam with the distributed braided piezoelectric composite actuator is presented to study its driving capability. Based on the piezoelectric constitutive equations and Euler–Bernoulli beam theory, the governing equation of the piezoelectric laminated beam is derived. The least-squares method for the piezoelectric laminated beam is established to solve the derived governing equation. The current approach is validated by comparison with published results and finite element results. In the numerical examples, the effects of the number and spacing of the three-dimensional braided piezoelectric composite patches, actuator central location, actuator length, actuator thickness ratio, cantilever beam thickness, applied voltage and fiber volume fraction on the driving capability of the distributed braided piezoelectric composite actuator are investigated. This study suggests the potential use of the distributed braided piezoelectric composite actuator in intelligent structures and provides useful guidance for the design and optimization of piezoelectric actuators.

A hybrid electro-responsive SWNT/PEDOT: PSS-based membrane towards soft actuator applications

The flexible soft actuators of conducting polymers can directly convert electrical stimulus into mechanical motions, which can be used for robotics and biomimetic applications. Herein, an electro-responsive membrane actuator based on poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate), functionalized single-walled carbon nanotube was fabricated using solution casting method with poly(vinyl alcohol) as a base intermediate polymer membrane. The poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) was evenly ornamented onto the single-walled carbon nanotube/poly(vinyl alcohol) membrane (single-walled carbon nanotube/ poly(vinyl alcohol)/ poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate)) surfaces through dip coating and verified by scanning electron and transmission electron microscopy analysis. The desirable bending response of the fabricated single-walled carbon nanotube/ poly(vinyl alcohol)/poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) membrane with time at different voltages and generated tip force makes it a promising material as a new-generation conductive polymer-based soft actuator. A permutation of the electrical conductivity, more surface area, and admirable electromechanical properties of the single-walled carbon nanotube/poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) components consequences in the composite electrode exhibited excellent actuation performance compared to the ionic polymer-metal composite actuators with Pt electrodes surface. The fabricated actuator membrane can be employed for artificial muscles, robotics, and other bio-mimetic applications.

Property of Nafion-ionic polymer-metal composites based on Mori–Tanaka methodology and gradient mechanics

Ionic polymer-metal composite (IPMC) actuators are a class of electroactive polymer composites that exhibit some interesting electromechanical characteristics such as low voltage actuation, large displacements, and benefit from low density and elastic modulus. Elastic modulus and surface resistance are basic properties of IPMCs that play a role in almost all practical applications of these materials. The prediction of the elastic modulus and surface resistance is of extreme importance to better grasp the mechanical behavior of IPMCs and to evaluate the success of the design. This paper has proposed a theoretical framework for predicting the elastic modulus and surface resistance of copper electrodes IPMCs. A five layers analytical assemblage model is introduced for the IPMCs relied upon improved classical lamination theory. The depositional metallic atoms were used as the exterior layer, the ionic polymer was used as the middle layer, and the material between the two layers was a gradient layer. Based on Mori–Tanaka methodology and gradient mechanics, the overall elastic properties of composites are obtained and lie between those obtained from the experiment. The prediction showed a good agreement with the experimental elastic modulus values with a maximum deviation of less than 10%. The overall results have provided useful insight into the elastic modulus and surface resistance effects to the properties of the IPMC. This would open further opportunities toward the higher application of IPMC.

A recurrent neural network–based model for predicting bending behavior of ionic polymer–metal composite actuators

The high application potential of ionic polymer–metal composites has made the behavior identification of this group of smart materials an attractive area. So far, several models have been proposed to predict the bending of an ionic polymer–metal composite actuator, but these models have some weaknesses, the most important of them are the use of output data (in autoregressive models), high complexity to achieve a proper precision (in non-autoregressive models), and lack of compatibility with the behavioral nature of the material. In this article, we present a hybrid model of parallel non-autoregressive recurrent networks with internal memory cells to overcome existing weaknesses. The validation results on experimental data show that the proposed model has acceptable accuracy and flexibility. Moreover, simplicity and compatibility with the behavioral nature of the material promote using the proposed model in practical applications.

Design of shape memory alloy sandwich actuators: an analytical and numerical modelling approach

Shape memory alloy (SMA)-based actuator composites are characterised by a high force output which is activated by a temperature increase. In this work we exploit this property to design sandwich structures with SMA-matrix composite actuator skins capable of exhibiting a reversible, tailored flexural response. A theoretical model which predicts the resultant deflection and flexural moment produced as a result of selectively actuating one of the system skins was developed and confirmed using a multi-step Finite Element (FE) analysis which takes into account the fabrication pathway through which these systems may be manufactured. The model correlates the geometric parameters and material properties of the various components making up the system and provides a quantitative description of the role which each variable plays in determining the overall sandwich actuator performance. This is necessary for the future production and implementation of such systems in real-life applications.

Modal characteristics of a cantilever beam with the free-end immersed in a magnetorheological fluid

This paper presents modal characteristics of a flexible cantilever beam with its free-end immersed in a magnetorheological (MR) fluid. Immersing the beam in MR fluid allows to change boundary conditions of the free-end by controlling the magnetic field intensity across MR fluid. Hence, the modal characteristics of the beam, such as natural frequency are varied as a function of the magnetic field applied to MR fluid domain. First, a thin cantilever beam was manufactured according to a design comprising a macro fiber composite (MFC) actuator for the beam excitation. Then, the dynamic responses of the beam were measured under two conditions: the free-end vibrating in air and the free-end immersed in MR fluid with different magnetic field intensities. The changes in the dynamic characteristics, such as resonance frequency, damping ratio, and resonant amplitude were evaluated and compared for various conditions. A significant reduction in the natural frequency was observed when the free-end of the beam was immersed in MR fluid and changed further when coil current was applied. In addition, the multiphysics simulation of the system was performed using finite element method. The numerical results of the dynamic response of the system showed good agreement with experimental results.

Programmable and Thermally Hardening Composite Yarn Actuators with a Wide Range of Operating Temperature

AbstractActuators have wide applications in intelligent robots, deformable textiles, and wearable devices, wherein the fiber‐based coiled linear actuators are particularly advantageous due to their good flexibility, high stress, and strain. However, their performances have been limited by the employed materials, whose microstructures are not easily designed and controlled. This article proposes a new approach of engineered composite yarns for the actuators. It leads to novel solutions to overcome these difficulties by offering wide design options in material properties and device structures. Here, an engineering design of programmable and thermally‐hardening helical composite yarn actuators (HCYAs) with a wide range of operating temperature is exemplified. Polyimide (PI) and polydimethylsiloxane (PDMS) are selected to fabricate HCYAs, achieving tensile actuation of 20.7% under 1.2 MPa from −50 °C to 160 °C and competitive specific work (158.9 J kg‐1, four times of natural muscle). With constant tensile deformation, PI/PDMS HCYA nearly tripled the stress from 20 °C to 100 °C. Moreover, it is surprisingly observed an unusual thermal‐hardening phenomenon that the tensile stiffness of the PI/PDMS HCYAs increases with the rise of temperature. Equipped by electrothermally powered PI/Cu/PDMS HCYAs, robotic hands and pressure‐tunable compressive bandage are demonstrated for their potential applications in robots and wearable devices.

Cooperative Optimal Collision Avoidance Laws for a Hybrid-Tailed Robotic Fish

This brief addresses the problem of collision avoidance by robotic fish that have a single caudal fin. The fish is hybrid-tailed in that the caudal fin is driven by a double-jointed mechanism. One joint is driven by a servomotor and the second joint is driven by an ionic polymer-metal composite (IPMC) actuator, which is often called an artificial muscle. For this type of robotic fish, collision avoidance is performed by employing a collision cone approach. Within the framework of the collision cone approach, Lyapunov-based methods are employed to determine analytical expressions of nonlinear guidance laws with which cooperative collision avoidance can be achieved. It is shown how these cooperative collision avoidance laws can be made optimal in the sense of minimizing an energy-like performance index. The conditions under which the developed guidance laws are robust to sensor measurement errors are determined. Simulations and experiments are performed to validate the guidance laws.

PF-IPMC: Paper/Fabric Assisted IPMC Actuators for 3D Crafts

An ionic polymer metal composite (IPMC) actuator is one of the most promising electroactive polymer devices. It is a lightweight and flexible actuator that can be operated in low voltage, high-frequency bandwidth, and even water. To widen the application field and enhance the potential of the IPMC actuator, a stable and flexible arbitrary 3D fabrication method is required. To address this arbitrary 3D fabrication problem, we have proposed and studied a novel fabrication method using papers and fabrics as the base materials of IPMC actuators. In this letter, we propose a novel paper/fabric (PF)-IPMC and its detailed fabrication process. For future design optimization, the fundamental characteristics derived from a type of paper and fabric are also determined through experiments. PF-IPMCs created from papers (Tissue, Kimwipe, and Kimtowel) have a greater ability for deformation, blocking force, and adsorption ratio than those created from fabrics (cotton and polyester). After the fundamental properties were evaluated, an origami plane and a crane PF-IPMC robots were created using the proposed method. Both PF-IPMC robots retained their initial shapes after completion of the fabrication process and could be operated normally. This shows the potential of the PF-IPMC for application to 3D craft.

Microtentacle Actuators Based on Shape Memory Alloy Smart Soft Composite

AbstractRecent advances in miniature robotics have brought promising improvements in performance by leveraging the latest developments in soft materials, new fabrication schemes, and continuum actuation. Such devices can be used for applications that need delicate manipulation such as microsurgery or investigation of small‐scale biological samples. The shape memory effect of certain alloys is one of the promising actuation mechanisms at small scales because of its high work density and simple actuation mechanism. However, for sub‐millimeter devices, it is difficult to achieve complex and large displacement with shape memory alloy actuators because of the limitation in the fabrication process. Herein, a fabrication scheme for miniaturized smart soft composite actuator is proposed by utilizing two‐photon polymerization. The morphing modes are varied by changing the direction of the scaffold lamination. In addition, the actuation is controlled via local resistive heating of a carbon nanotube layer deposited inside of the actuators. The proposed design can generate a 390 µN force and achieve a bending angle up to 80°. Applications of the actuators are demonstrated by grasping small and delicate objects with single and two finger devices.

Analytical modeling of laminated composite plates integrated with piezoelectric layer using Trigonometric Zigzag theory

The analytical solution for static analysis of laminated composite plate integrated with piezoelectric fiber reinforced composite actuator is obtained using a recently developed Trigonometric Zigzag theory. The kinematic field consists of five independent field variables accommodating non-linear variation of transverse shear strains through the thickness of the laminated composite plate. The principle of minimum potential energy is adopted to derive the governing equations of equilibrium. Navier’s solution technique is employed to convert the system of coupled partial differential equations into a system of algebraic equations. The electric potential is assumed to vary linearly through the thickness of the piezoelectric layer. The analytical formulation also does not include voltage as an additional primary variable. The response in the form of deflection and stresses are obtained for smart composite plates subjected to electro-mechanical loads and compared with the elasticity solutions and available results reported by other researchers in the existing literature. The transverse shear stresses are accurately determined by an efficient post-processing technique of integrating the equilibrium equations of elasticity. Parametric studies on actuation in the response of the smart composite plate are also presented graphically in order to have a clear understanding of the static behavior.

New Efficient Technique for Finite Element Modeling of Macro Fiber Composite Piezoelectric Materials

A lot of interest to simulate piezocomposite actuators with finite element method has been increased recently. However, there are still open questions regarding the modeling methodology, accuracy, and computational time cost. In this work, a new technique for modeling macro fiber composite piezoelectric actuator by finite element analysis is proposed. The presented technique models the piezocomposite actuator as a simple monolithic piezoceramic material with just two electrodes along its longitudinal extremes instead of using the actual large number of electrodes which results in very fine finite element mesh with high computational time cost. The proposed technique is validated successfully by comparing its results with those of the actual detailed model as well as with the published experimental results and manufacturer’s data.

Stimuli-responsive composite biopolymer actuators with selective spatial deformation behavior

Bioinspired actuators with stimuli-responsive and deformable properties are being pursued in fields such as artificial tissues, medical devices and diagnostics, and intelligent biosensors. These applications require that actuator systems have biocompatibility, controlled deformability, biodegradability, mechanical durability, and stable reversibility. Herein, we report a bionic actuator system consisting of stimuli-responsive genetically engineered silk-elastin-like protein (SELP) hydrogels and wood-derived cellulose nanofibers (CNFs), which respond to temperature and ionic strength underwater by ecofriendly methods. Programmed site-selective actuation can be predicted and folded into three-dimensional (3D) origami-like shapes. The reversible deformation performance of the SELP/CNF actuators was quantified, and complex spatial transformations of multilayer actuators were demonstrated, including a biomimetic flower design with selective petal movements. Such actuators consisting entirely of biocompatible and biodegradable materials will offer an option toward constructing stimuli-responsive systems for in vivo biomedicine soft robotics and bionic research.

Displacement response of ionic polymer metal composite actuator to asymmetric square waves in air operating

Ionic Polymer Metal Composite (IPMC) is a novel electrical actuated intelligent material with the advantages of low driving voltage, large bending displacement, high flexibility, low density and so on. It has been used as an intelligent driving material with prospective applications for robot fish and bionic organ, and is expected to be used out of water. As an important and applicable characteristic, displacement response of IPMC has drawn tons of researchers’ attentions. In this paper, the asymmetric square waves with variable frequencies, low level voltages, and duty cycles were employed to drive IPMC samples, the displacement responses were investigated and analyzed. The control mode of IPMC sample was obtained using curve fitting of step response. By combining Bode plot of IPMC system with the Fourier transform of square waves, the effect of parameters changes to the displacement response were analyzed and discussed, and the potential application of the asymmetric displacement is illustrated and proposed by a capsule like underwater robot.

Nonlinear Analysis of Laminated Beams with Braided Fiber Piezoelectric Composite Actuators

This paper presents a novel approach for improving the reliability and driving capability of piezoelectric actuators by developing braided fiber piezoelectric composite (BFPC) actuators. The nonlinear analysis of laminated beams integrated with the BFPC actuators under electric load is presented. According to Timoshenko beam theory and von Kármán nonlinear geometric relation, the strain components of the piezoelectric laminated beams are obtained. The nonlinear governing equations of the piezoelectric laminated beams are derived by the Galerkin method and principle of minimum potential energy, and then are solved through the direct iterative method. The accuracy of this method is demonstrated by its comparison with the published results. The driving capability of the BFPC actuator and the existing piezoelectric composite actuator is compared. The influences of the fiber volume fraction, actuator thickness, simply supported beam thickness and applied voltage on the driving capability of the BFPC actuators are discussed through a comprehensive parametric study. The numerical results illustrate that the BFPC actuators with excellent driving capability can effectively control the deformation of smart structures.

Robust super-twisting sliding mode controller with state observer for position tracking of ionic polymer–metal composite actuators

To date, a novel class of smart materials, known as ionic polymer–metal composites, have been intensively studied because of their huge potential applications in robotics, microelectromechanical systems, biomedical devices, and artificial muscles. The position tracking control of the ionic polymer–metal composite actuators is one of the challenging tasks due to the highly nonlinear, uncertain, and unmodeled dynamics. These inaccurate and unmodeled dynamics cause the unwanted disturbances which reduce the control performance. Therefore, a robust feedback controller for position tracking of the ionic polymer–metal composite actuators is necessary. To address this issue, this article presents a super-twisting sliding mode controller combined with integral-chain differentiator as state observer. The main advantage of the proposed method is its potential to estimate the states of the system continuously. As a result, the controller not only eliminates the parameter uncertainties and external disturbance but also it can overcome the chattering problem. The results confirm the feasibility and efficiency of the proposed method both in simulation and experiment.

Analysis of Novel Morphing Trailing Edge Flap Actuated by Multistable Laminates

This paper presents an analysis of a novel morphing trailing edge flap design for a wind turbine rotor blade with embedded multistable composite plates. Morphing trailing edge devices are promising candidates for reducing loads in variable wind conditions and turbulent flows as well as capable of changing the shape rapidly. The application of multistable laminates allows large deformations with modest actuation demand, without the need for a continuous supply of energy. They can undergo snap-through with the help of Macro Fiber Composites actuator patches. A rectangular multistable plate is designed with the optimal location of actuators, aiming at two-way snap-through without the loss of bistability. A multi-objective derivative-free optimization scheme is used to minimize the snap-through voltages and maximize the out-of-plane displacements. The designed multistable plates with actuators are embedded at a suitable location of the morphing trailing edge flap. As the multistable plates snap, the flap deflects to a new position. The mechanism of the new morphing concept is simulated and analyzed with finite element tools.

Fast, Light-Responsive, Metal-Like Polymer Actuators Generating High Stresses at Low Strain

Summary Producing lightweight polymeric actuators able to generate high stresses typical of hard metals and/or ceramics remains challenging. The photo-mechanical responses of ultra-drawn ultra-high molecular weight polyethylene (UHMWPE) actuators containing azobenzene photo-switches with symmetrically attached polyethylene (PE) side chains are reported. Long PE side chains promote dispersion within the apolar UHMWPE matrix, and the ultra-drawn films are highly aligned. The ultra-drawn azobenzene-doped UHMWPE films have high Young's moduli (∼100 GPa) and are viscoelastic at room temperature at strains below 1%. The photo-mechanical response of the films is fast ( 6 × 104 Pa (kg m−3)−1) to UV or visible light at a low strain (∼0.06%). The actuator responds to rotating linearly polarized light, causing a photo-induced stress wave response. Such rapid, high-stress, low-strain, photo-mechanical responses are unique in soft polymer systems with physical values approaching hard metals/ceramics.